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# os
This is a hobby OS based on a microkernel.
It currently supports:
1. Basic preemptive multitasking with task states & exiting.
2. Physical & virtual memory management
3. Interrupts.
4. The PIT, used to do preemption.
5. The serial port, used as an output for logs. (driver in kernel, will eventually be moved out)
## Building (on Linux or Mac)
To build the OS, you will need a custom patched GCC cross-compiler targeted for my OS, and GRUB.
Installing GRUB on:
1. Ubuntu. GRUB is already installed.
2. Another linux distro. GRUB is likely already installed, but if it is not, you will need to use your distribution's package manager to install GRUB.
3. Mac. You will need to install Homebrew, then install the formula i386-elf-grub.
### Building the cross-compiler
The instructions for building a cross compiler are [here](https://wiki.osdev.org/GCC_Cross-Compiler), though a few changes need to be made.
First, you **must** download GCC 9.2.0 and Binutils 2.32, or the patches may not apply correctly.
Next, you need to apply the patches located in the patches/ directory.
Set $TARGET to i386-myos, not i686-elf.
When running configure for both Binutils and GCC, you must pass --sysroot=<path to cloned github repo>/sysroot as an extra argument,
otherwse the compiler will not be able to find the libc headers.
Otherwise, the build is as normal.
Once the cross-compiler is built, the OS can be built by simply typing `make`.
## Additional setup for development
To properly develop the OS, you willl need to install QEMU and GDB.
Installing QEMU on
1. Ubuntu. Run `sudo apt get install qemu`
2. Another linux distro. Use your distribution's package manager to install QEMU.
3. Mac. Run `brew install qemu`
Installing GDB on
1. Ubuntu. Run `sudo apt get install gdb`
2. Another linux distro. Use your distribution's package manager to install GDB.
3. Mac. Run `brew install gdb` (Note: It will warn about an unsigned binary, but this will have no impact on debugging the OS)
After this, you can run the OS in QEMU by typing `make run`, and start a remote debugging session by typing `make debug`.
The serial port output of the OS is redirected to a file callled serout in the main directory.